1. Field of the Invention
This invention relates to the production of alkylene glycols by heterogeneous catalysis from alkylene oxides and water using hydrothermally stable catalysts. The invention also relates to a new class of hydrothermally stable mixed metal framework compositions. The new compositions are useful as catalysts for preparing alkylene glycols from alkylene oxides using either liquid or vapor phase hydrolysis.
2. Description of Related Art
Commercial processes for preparing alkylene glycols, for example, ethylene glycol, propylene glycol and butylene glycol, involve liquid-phase hydration of the corresponding alkylene oxide in the presence of a large molar excess of water (see, for example, Kirk-Othmer, Encyclopedia of Chemical Technology, Vol. 11, Third Edition, page 939 (1980)). The hydrolysis reaction typically is conducted at moderate temperatures, e.g., from about 100.degree. C. to about 200.degree. C., and elevated pressures with water typically being provided to the reaction zone in excess of 15 moles per mole of alkylene oxide. The primary by-products of the hydrolysis reaction include di- and polyglycols, e.g., dialkylene glycol, trialkylene glycol and tetra-alkylene glycol. The di- and polyglycols are believed to be formed primarily by reaction of alkylene oxide with alkylene glycol, as alkylene oxides are generally more reactive with alkylene glycols than they are with water. The large excess of water is employed in order to favor the reaction with water instead and thereby obtain a commercially-attractive selectivity to the monoglycol product.
Due to the large excess of water, recovery of alkylene glycol from the hydrolysis reaction mixture is very energy intensive. Typically, water is removed by evaporation to leave an alkylene glycol-containing residue which is purified further by distillation. A process which would permit a reduction in the amount of water employed while maintaining, or enhancing selectivity toward the monoglycol product would be highly desirable.
While the hydrolysis reaction can proceed uncatalyzed, the presence of acids or bases enhances the rate of reaction. Acid and base catalysts do have shortcomings, however. For instance, base catalysts generally do not beneficially affect selectivity to the formation of the monoglycol product and the use of acid catalysts typically is accompanied by corrosion problems. Hence, commercial processes typically utilize relatively neutral hydrolysis conditions (for instance, pH 6-10).
Representative of the numerous acid catalysts that have been suggested for use in hydration of alkylene oxides include fluorinated alkyl sulfonic acid ion exchange resins (U.S. Pat. No. 4,165,440, issued Aug. 21, 1979); carboxylic acids and halogen acids (U.S. Pat. No. 4,112,054, issued Sept. 5, 1978); strong acid cation exchange resins (U.S. Pat. No. 4,107,221, issued Aug. 15, 1978); aliphatic mono- and/or polycarboxylic acids (U.S. Pat. No. 3,933,923, issued Jan. 20, 1976); cationic exchange resins (U.S. Pat. No. 3,062,889, issued Nov. 6, 1962); acidic zeolites (U.S. Pat. No. 3,028,434, issued Apr. 3, 1962); sulfur dioxide (U.S. Pat. No. 2,807,651, issued Sept. 24, 1957); trihalogen acetic acids (U.S. Pat. No. 2,472,417, issued June 7, 1949); and copper-promoted aluminum phosphate (U.S. Pat. No. 4,014,945, issued Mar. 29, 1977).
In addition to the acid catalysts, numerous other catalysts have been suggested for the hydration of alkylene oxides in the presence of carbon dioxide. These include alkali metal halides, such as chlorides, bromides and iodides; quaternary ammonium halides such as tetramethyl ammonium iodide and tetramethyl ammonium bromide (British Pat. No. 1,177,877); organic tertiary amines such as triethylamine and pyridine (German published patent application No. 2,615,595, Oct. 14, 1976, and U.S. Pat. No. 4,307,256, issued Dec. 22, 1981); quaternary phosphonium salts (U.S. Pat. No. 4,160,116, issued July 3, 1979); chlorine or iodine-type anion exchange resins (Japanese Kokai No. 57/139,026, published Aug. 27, 1982); and partially amine-neutralized sulfonic acid catalyst, e.g., partially amine-neutralized sulfonic acid resin (U.S. Pat. No. 4,393,254, issued July 12, 1983).
Various metal-containing compounds, including metal oxides, also have been proposed as catalysts for the hydrolysis of alkylene oxides. For example, U.S. Pat. No. 2,141,443, issued Dec. 27, 1938, discloses the production of glycols by reacting alkylene oxide with water in the presence of a dehydrating metal oxide, for example, alumina, thoria, or oxides of tungsten, titanium, vanadium, molybdenum or zirconium. The reaction is carried out in the liquid phase and under conditions of temperature and pressure suited to maintain such phase. In example 7, the patentees disclose rendering a yellow tungstic acid catalyst more mechanically stable by admixture with a mixture of silicon ester, alcohol and water, followed by drying the catalyst. Similarly, U.S. Pat. No. 2,807,651, issued Sept. 24, 1957, states that it is known to catalyze the reaction of alkylene oxide and water using alkali metal bases, alcoholates, and oxides of titanium, tungsten and thorium.
Many metals such as vanadium, molybdenum, tungsten, titantium, chromium, zirconium, selenium, tellurium, tantalum, rhenium, uranium and niobium, also have been proposed as components for catalysts for preparing 1,2-epoxides of alpha-olefins and organic hydroperoxides and often are present during a subsequent hydrolysis reaction. For instance, Examples I and III of U.S. Pat. No. 3,475,499, issued Oct. 28, 1969, disclose that a mixture of normal alpha-olefins containing 11 to 15 carbon atoms was epoxidized with ethylbenzene hydroperoxide in the presence of molybdenum naphthenate catalyst. After distillation, the bottoms, which contained the 1,2-epoxides and the molybdenum-containing catalyst, were contacted with water containing 0.5 percent sodium hydroxide at a temperature of 90.degree. C. That reaction product was distilled and a conversion of 1,2-epoxides was reported to be 100 percent and the selectivity to 1,2-glycols was reported to be 94 percent.
More recently, U.S. Pat. No. 4,277,632, issued July 7, 1981, discloses a process for producing alkylene glycol by hydrolysis of alkylene oxide in the presence of a catalyst of at least one member selected from the group consisting of molybdenum and tungsten. The catalyst may be metallic molybdenum or metallic tungsten, or inorganic or organic compounds thereof, such as oxides, acids, halides, phosphorous compounds, polyacids, alkali metal and alkaline earth metal, ammonium salts and heavy metal salts of acids and polyacids, and organic acid salts. An objective of the disclosed process is stated to be the hydrolysis of alkylene oxides wherein water is present in about one to five times the stoichiometric value without forming appreciable amounts of by-products such as the polyglycols. The reaction may be carried out in the presence of carbon dioxide. When the reaction is carried out in the presence of nitrogen, air, etc., the patentees state that the pH of the reaction mixture should be adjusted to a value in the range of 5 to 10. Japanese Kokai No. JA 54/128,507, published Oct. 5, 1979, discloses a process for producing alkylene glycols from alkylene oxides and water using metallic tungsten and/or tungsten compounds.
Japanese Kokai No. 56/073,035, published June 17, 1981, discloses a process for the hydrolysis of alkylene oxide in the presence of a carbon dioxide and a catalyst consisting of a compound containing at least one element selected from the group of titanium, zirconium, vanadium, niobium, tantalum and chromium. The compounds include the oxides, sulfides, acids, halides, phosphorous compounds, polyacids, alkali metal salts of acids and polyacids, ammonium salts of acids and polyacids, and heavy metal salts of acids.
Japanese Kokai No. 56/073,036, published June 17, 1981, discloses a process for the hydrolysis of alkylene oxide in the presence of a carbon dioxide atmosphere and a catalyst consisting of a compound containing at least one element selected from a group comprising aluminum, silicon, germanium, tin, lead, iron, cobalt and nickel.
Japanese Kokai No. 56/92228, published July 25, 1981, is directed to processes for producing highly pure alkylene glycols. The disclosure is directed to a distillation procedure for recovering a molybdenum and/or tungsten-containing catalyst from an alkylene oxide hydrolysis product in the presence of carbon dioxide. The application states that the catalyst is at least one compound selected from the group consisting of compounds of molybdenum and tungsten which compound may be in combination with at least one additive selected from the group consisting of compounds of alkali metals, compounds of alkaline earth metals, quaternary ammonium salts and quaternary phosphonium salts. The preferred catalysts are stated to be molybdic acid, sodium molybdate, potassium molybdate, tungstic acid, sodium tungstate and potassium tungstate. Potassium iodide is the only additive employed in the examples. For a similar disclosure see also Japanese Kokai No. 56/90029.
U.S. Pat. No. 4,551,566--J. H. Robson and G. E. Keller, discloses producing monoalkylene glycols with high selectivity by reacting a vicinal alkylene oxide with water in the presence of a water-soluble vanadate. Lower water to alkylene oxide ratios can be employed using the disclosed process with attractive selectivities to monoglycol products. The counter ion to the vanadate is selected to provide a water-soluble vanadate salt under the reaction conditions employed and alkali metals, alkaline earth metals, quaternary ammonium, ammonium, copper, zinc, and iron are suggested cations. It also is disclosed that the vanadate may be introduced into the reaction system in the salt form or on a support such as silica, alumina, zeolites and clay. Since the vanadate ion is water-soluble, it can be lost from the reaction system and means must be provided to recover it from the effluent from the reaction zone. In U.S. Pat. No. 4,578,524, the reaction of alkylene oxide and water to form monoalkylene glycol is carried out in the presence of a dissociatable vanadate salt and carbon dioxide.
Unfortunately, insoluble salts of metavanadate, such as calcium metavanadate, as well as insoluble molybdate, tungstate, etc., and other metalate salts do not appear to provide the selectivity enhancement toward the monoglycol products which is achievable with the water-soluble salts. Hence, problems with the recovery of the water-soluble salts are significant factors in considering the use of the technology on a commercial scale.
U.S. Pat. No. 4,667,045--J. R. Briggs and J. H. Robson discloses producing alkylene glycols with high selectivity from alkylene oxides and water, either as a liquid or vapor, in the presence of organosalts of a metalate anion having at least one cyclic alkylenedioxy moiety. Particularly preferred metals for the metalate anions are vanadium, molybdenum and tungsten.
European Patent Publication 160,330 describes a process for making alkylene glycols from alkylene oxide and water in the presence of a metalate anion which is associated with an electropositive complexing site on a solid support, such as an anion exchange resin. Again, metalate anions of the metals vanadium, molybdenum and tungsten are preferred.
Japanese Kokai No. 48/22406 discloses using calcium apatite as either a liquid or vapor phase hydrolysis catalyst for making alkylene glycol from alkylene oxide, such as ethylene oxide.
Japanese Kokai No. 55/69525 and Japanese Kokai No. 57/106631 disclose using hydrotalcite (Mg.sub.6 Al.sub.2 (OH).sub.16 CO.sub.3.4H.sub.2 O) and its analogs where magnesium is replaced by calcium, zinc, copper or nickel; aluminum is replaced by iron or chromium, and carbonate is replaced by chloride, bromide, fluoride, nitrate, acetate, cyanate, sulfate, chromate, oxalate, phosphate or ferrocyanate, with the stoichiometry adjusted appropriately, as a catalyst for preparing ethylene glycol by reacting ethylene carbonate and water. The disclosures note that these hydrotalcite-type catalysts are easily separated from the liquid reaction medium and are stable under the hydrolysis reaction conditions (130.degree. C.-160.degree. C.). Other catalysts for hydrolyzing alkylene carbonates also are disclosed in Japanese Kokai No. 58/150435 (a zinc compound supported on an alumina or silica-alumina carrier) and Japanese Kokai No. 58/159849 (a copper compound supported on an alumina or silica-alumina carrier).